Similar to the hard choices being made at all federal agencies for the President's Budget, NASA has dutifully reduced costs, but as a consequence is reducing missions.
All of the NASA budget presentations and handouts are available at their website, but it is difficult to understand what the agency is not going to do.
Obama's budget would cut Mars program, solar system exploration tells that the cuts will cost two joint missions to Mars with the European Space Agency (ESA). The 2016 mission, Trace Gas Orbiter was planned to survey the Martian atmosphere. The 2018 mission would have landed a rover to collect rocks and return the samples to Earth.
Aside from the austere federal budget in general, NASA has two problem children: The James Webb Space Telescope and the Space Launch System (SLS). The new space telescope is substantially over budget, with continuing cost and schedule risks. The new heavy lift rocket and crew vehicle were mandated by Congress rather than a strong ownership by NASA.
I apologize for the quality of the graphic below, but I predict it will generate another fight with Congress. NASA continues to press for funding commercial space exploration, while Congress considers national space technology more relevant. In 2012 through 2015, note all of the commercial launches of SpaceX and Orbital. My guess is that Congress will tell NASA to focus on its own Space Launch System and let would-be commercial space operators fund their own way.
NASA Launch Schedule - from the FY12 Summary Budget Briefing
Mmm. I believe NASA and the Department of Energy represent the big engineering and science projects that the national government should fund. Although it overlaps with the Department of Transportation, I would like additional research and development on new aviation technology. The U.S. is particularly dependent upon aviation for transportation, and we need 'to break glass' with advancements that are too risky for commercial companies.